Battery systems, in particular traction batteries for hybrid electric vehicles/electric vehicles, generally comprise one or more battery cells (or battery cell blocks) connected in series. The battery cells are operated only within certain voltage limits, since they otherwise age significantly more quickly or even cause a thermal reaction. This thermal reaction, for example in the form of a fire, should be avoided. Owing to different manufacturing tolerances and different aging processes, the individual battery cells also have fluctuations in their charge capacitances and internal resistances. On account of the series circuit, the different charge capacitances and the different internal resistances again lead to the battery cells being charged and discharged differently and, in extreme cases, being able to occupy critical states of charge (for example due to overcharging).